Trip wires are most well known for setting off explosives but in this case you'll be setting up a low-voltage piezo alarm to let you know when a trespasser is in your home or if your teenager is trying to get in your gun case or liquor cabinet.

Advertisement

Instructables user EngineeringShock designed his trip wire to be simple, safe, and affordable. You'll need a DC piezo buzzer or siren, a 10k Ohm resistor, an NPN transistor, two nails, 4 AA batteries and a battery pack, and an extremely thin wire to act as the trigger. EngineeringShock used thin gauge magnet wire.

You'll need to have a soldering iron as well, and the complete wiring diagram can be found at the source link below.